X.25 Link Configuration Parameters

This is a list of the X.25 link parameters and their default values.

The following parameters are sorted alphabetically by parameter name. Upper and lower case characters do not affect the sort sequence. Numbers occur before letters. Each parameter is followed by its default value, followed by an explanation of its effect.

Parameter
Keyword Default
Value Description

bcug YES Flag. Allows use of the Bilateral Closed User Group selection facility in Incoming Call and Call Request packets. If the flag is not YES, calls containing this facility are cleared.

bwc_first 1 Starting Logical Call Identifier (LCI) for both-way logical channels. Normally 1, but will be larger if the network uses Logical Channel Groups to differentiate between virtual circuit (VC) types, or if permanent virtual circuits (PVCs) are in use.

bwc_num 8
Numeric field contains the number of both-way logical channels. You can select the starting logical channel number to allow for networks which use a logical channel group number to distinguish between types of logical channels, and networks which allow logical channel numbers to be non- contiguous.

Unless there is a very good reason to do so (like your PTT administration told you it had to be that way), configure ALL your logical channels as "both way".

You can allocate logical channels as any mixture of one-way incoming only (can only be used for taking calls), both way (no restriction on making or taking calls), or one-way outgoing only (can only be used for making calls). If you must use one-way channels, you must follow the CCITT convention when selecting channel numbers. A DTE always chooses the highest-numbered free logical channel for outgoing calls, and a DCE always chooses the lowest-numbered free logical channel for outgoing calls.

Thus, for DTE, the following logical propositions must be true:

0 < numpvcs
numpvcs < owi_first
owi_first + owi_num < bwc_first
bwc_first + bwc_num < owo_first
owo_first + owo_num < 4096

For DCE, the propositions are slightly different:

0 < numpvcs
numpvcs < owo_first
owo_first + owo_num < bwc_first
bwc_first + bwc_num < owi_first
owi_first + owi_num < 4096

called_length 8 Indicates how much of Incoming Call's Called Network Address field is to be interpreted as your system's Network Address. The remainder of the Called Network Address is parsed as the subnet Address (SNA).

clam NO DTE/DCE Independent Flag. Called Line Address Modification Notification facility. Allows use of this facility in Call Accepts and Clears.

class_neg YES Flag. Allows throughput class negotiation for incoming calls.

class_recv 12
Default inbound throughput class. Both inbound and outbound throughput class are set artificially high (48 Kbps) to avoid problems with incoming calls being cleared because they are requesting a higher throughput class than the default configuration.

When force_negotiate is YES, this may cause problems with Call Accept/Connect packets being cleared by a DCE which knows that a value of 12 is too large.

The following table maps throughput class values to speeds:

Parameter Value Baud Rate

7
8
9
10
11
12
13

1200 bps
2400 bps
4800 bps
9600 bps
19200 bps
48000 bps
64000 bps

class_send 12 Default outbound throughput class.

cug YES Flag. Allows use of the Closed User Group selection facility in Call Request or Incoming Call packets.

dbitmod NO DTE/DCE Sensitive Flag. As DCE, causes D-bit stripping (out) and inserting (in). This is what CCITT calls the D Bit Modification Facility. As DTE, you set this flag to request D Bit Modification of the DCE in Registration.

diagnostics YES DTE/DCE Independent Flag. Enables transmission of diagnostic packets. Generally YES (on) for DCEs and NO (off) for DTEs.

dial_defn
This field is used to define a dial definition for synchronous and asynchronous X.32 (dial-up) modes. The following are elements of a dial definition:

dial_string

connect_string

number_of_retries

timeout_between_retry

init_string

These are defined in detail in Dial-up X.25 (X.32) Configuration.

dna blank This field defines the calling data network address that is included in an SVC call request. Up to 16 digits may be specified. The default is to leave this parameter blank (meaning that a calling dna is not specified).

dte YES Flag. YES for DTE X.25 protocol, NO for DCE X.25 protocol. dte controls how the protocol behaves. As a DTE, it sends HDLC commands on Address B (01), and responses on address A (03), while a DCE sends commands on address A (03) and responses on address B (01). When connecting to a public data network, the attached computer should always be DTE. The choice of DTE/DCE also affects both logical channel selection for outgoing Call Requests, and packet level registration behaviour.

DXEsupport 0 Flag. Controls how the software treats an incoming telephone call in an X.32 (Dial-up) environment. 1 (yes) for switching DTE/DCE operation on the basis of call origination, 0 (no) for normal operation. When DXE support is on (DXESupport=YES), the mode of operation is switched to act as DCE when it receives a telephone call from another machine, and acts as DTE when it originates (dials out) a telephone call. It overrides the dte flag.

fastselect NO Flag. Allows use of the Fast Select Facility in Call Request and Incoming Call packets. If disabled (NO), packet level clears incoming and outgoing Fast Select calls.

force_negotiate YES Flag. If YES, call setup packets that are sent (Call Request/Incoming Call and Call Accept/Call Connect) always contain the default flow control negotiation values (throughput class, packet size, and packet window size). The X.25 software fills these in even if the application does not request negotiation. Of course, only the facilities allowed (such as by size_neg=YES) are inserted. YES is CCITT standard. Use NO with Dynapac X.25 switches.

frm_extseq 0 Flag. If specified as 0, the frame level uses standard (modulo 8) sequence numbering. If 1, the frame level uses extended (modulo 128) frame sequence numbers, and values for the parameter k may be between 1 and 127.

incallbarred NO DTE/DCE Independent Flag. Incoming calls are barred.

k 7 Numeric field contains the Frame Level (HDLC) window size. The maximum number of frames that the HDLC protocol allows to be outstanding at any time.

linkenable YES Flag. Controls whether or not the local node will attempt to bring an X.25 link up with this port. When YES (true), the X.25 software sets up the hardware to send flags, and the frame level continually tries to start the link, unless your system is DTE and the passive_frm parameter is set to YES. When NO (false), the hardware provides a DTR signal, but no flags are sent. Nothing is ever done on a disabled link.

modemid 0 Numeric field identifies the type of modem control language to use as follows:

0 For dedicated lines (non X.32)

1 CCITT V.25bis dialing (synchronous dial)

N1 519 Maximum frame size in bytes, including the frame and packet level headers, and the CRC bytes. This value should accommodate at least the maximum packet size to negotiate down to from the packet level parameters, but never less than 263 (for full option call setup packets).

N2 10 Numeric field contains the Frame Level (HDLC) retry count. This is the number of times that the HDLC protocol will retry an operation before indicating failure.

netid 6 Network identifier that identifies the public network to which your system is connecting. The netid affects national facilities parsing, and the mechanism that is used to set up an X.25 link. DM are sent to start up an enabled link, unless indicated otherwise below:

0 Datapac '76
Parses Datapac '76 facilities for collect calling and priority service.

1 Datapac '80
Parses Datapac '80 national facilities for NUI and priority service.

2 Telenet
No Telenet national facilities parsing. Starts up X.25 links by sending DISC, rather than DM. If passive_frm is also YES for DTEs, nothing is sent to start up the link. It is up to the remote system to start the link (usually, by sending SABM).

3 Vanilla 1980 network
As for Datapac '80, except no national facility parsing.

4 DATEX-P
No Datex-P national facility parsing. Starts up X.25 links by sending SABM, unless passive_frm is also YES and your system is DTE, in which case DM are sent at startup. The use of 1984 X.25 facilities is enabled.

5 KDD
Same as for Vanilla 1980.

6 Vanilla 1984 network
No national facility parsing. Allows CCITT 1984 facilities.

7 PSS
No PSS national facility parsing. Starts up X.25 links by sending DISC, rather than DM. If passive_frm is also YES for DTEs, nothing is sent to start up the link; the link must be initiated at the remote system.

8 Tymnet
Same as for Vanilla 1980.

9 BX25
BX.25 is an X.25 variant defined by AT&T. The X.25 software provides support for a selection of BX.25 facilities and capabilities (for example, T24 and T25). When netid is set up for BX.25, you can use the BX.25 facility for "Alternate Method of Password Exchange" at link setup.

10 Infoswitch
Same as for Vanilla 1980, except for link startup. The link is started up by sending SABM, unless passive_frm is also YES and your system is DTE, in which case DM are sent.

11 Infonet

12 Transpac
Allows use of logical channel number zero (0) for X.25 Switched Virtual Circuits.
Note: This is completely unrelated to netid as used by packetnets and the API.

no_local_
charging NO DTE/DCE Sensitive Flag. Local Charging Prevention. When YES (on), this overrides both the Reverse Charging and Reverse Charging Acceptance parameters. As DTE, this facility causes refusal of incoming calls with Reverse Charging and inserts Reverse Charging into outgoing calls without a NUI. As DCE, Local Charging Prevention rejects attempts to send outgoing calls with Reverse Charging, and inserts Reverse Charging in incoming calls without a NUI.

numpvcs 0 Numeric field contains the number of X.25 logical channels reserved for permanent virtual circuits. As per the X.25 specification, permanent virtual circuits begin with logical channel 1, and extend through to (and include) logical channel number numpvcs. See also the related field bwc_first.

outcallbarred NO DTE/DCE Independent Flag. Outgoing calls are barred.

owi_first 1 Numeric field contains the starting Logical Channel Identifier (LCI) for one-way incoming only channels.

owi_num 0 Numeric field contains the number of one-way incoming only logical channels.

owo_first 1 Numeric field contains the starting Logical Channel Identifier (LCI) for one-way outgoing only channels. Normally, there are none, so the default value for this parameter is 1.

owo_num 0 Numeric field contains the number of one-way outgoing only logical channels. Normally, there are none, so the default value for this parameter is 0.

passive_frm NO Flag that determines whether or not the local node will attempt to bring up the HDLC link. If YES, don't send SABM as DTE; the remote system must send it.

passive_pkt NO Do not initiate packet level startup (send a Restart Request packet) as DTE.

per_call_
chginfo NO DTE/DCE Sensitive Flag. Enables the 1984 CCITT standard charging information. As DCE, allows incoming call or call accepts to specify a charging information request, and outgoing clear or clear confirms to send the charging information. As DTE, allows outgoing requests and incoming charging information.

per_ifce_
chginfo NO DTE/DCE Sensitive Flag. Enables the 1984 CCITT standard charging information. As DCE, all outgoing clear or clear confirms are allowed to have this charging information. As DTE, allows incoming clear or clear confirms to have this charging information.

pkt_extseq NO Flag. Enables Modulo 128 (Extended) Packet Sequence Numbering.

pktreject NO DTE/DCE Sensitive Flag. Packet Level Reject. As DTE, the system generates packet rejects (PKT REJ) on bad P(S). As DCE, the system receives packet rejects (PKT REJ).

pktsize_max 256 Maximum packet size to automatically negotiate down to.

pktsize_neg YES Flag. Allows packet size negotiation in incoming calls.

pktsize_send 128 Default send packet size.

pktsize_recv 128 Default receive packet size.

registration NO DTE/DCE Sensitive Flag. CCITT 1984 Registration Packet support. As DTE, the system sends Registration Requests. As DCE, the system receives them.

recv_stats NO Flag. Indicates whether the system receives call statistics from the X.25 to which it is connected. This field is used to determine where to send Packet Level initiated Clears (for error conditions) to obtain call statistics. When YES (on), this flag causes the link to be cleared first. This parameter also enables diagnostics in incoming Datapac Clear Confirms.

rev_charging YES DTE/DCE Sensitive Flag. As DTE, allows outgoing calls to have Reverse Charging. As DCE, allows incoming calls to have Reverse Charging. This option is overridden if Local Charging Prevention is YES (on).

rev_charging_
accept
YES DTE/DCE Sensitive Flag. Reverse Charging Acceptance. As DTE, allows Reverse Charging on incoming calls. As DCE, allows Reverse Charging on outgoing calls. This option is overridden if Local Charging Prevention is YES (on).

rpoa NO Flag. Allows RPOA selection (like above).

rx_password blank
Expected BX25 password. This field is ignored if netid is not defined as BX25. If BX25 is configured, the "Alternate Method of Password Exchange" is used to transmit and receive a Password. If rx_password is not set (default), the frame level does not expect a password after link up. If a password is received, it would be treated as an I frame and passed unmodified to the packet level.

Control Characters may be encoded in octal.

String terminators: SPACE (\040), TAB (\010), CR (\015) and LF (\012) MUST be encoded in octal to be part of the password. The first character of this string is the number of bytes in the actual password, and is not part of the password. The maximum actual password length is 19. The configured password will be the actual I frame contents.

For example, the password "AMATCOLL BX25" is encoded as:
rx_password=\015AMATCOLL\040BX25

speed 0 Baud rate in bits per second. For an externally clocked link, enter 0. Enter 1200 for 1200 bps, 9600 for 9600 bps, and so on.
speed controls the frequency of the clock signal that is presented on the transmit clock output pin as defined by the electrical interface specification (RS-232, V.35, X.21, etc.). speed also controls whether or not it presents any signal on that pin (speed=0).

T1 3 Numeric field contains the frame level (HDLC) retry timer (in seconds). DO NOT set this value to less than the time required to transmit the longest packet (see N1),
based on the speed of this link.

T20 30 Restart Confirmation timer in seconds.

T21 30 Call Request timer in seconds (outgoing calls only).

T22 30 Reset Confirmation timer in seconds.

T23 30 Clear Confirmation timer in seconds.

T24 BX25 only, RR packet polling timer in seconds.

T25 BX25 only, reset unacknowledged data packets timer in seconds.

T28 30 Registration confirmation timer in seconds.

T3 0 If defined as 0, the link remains quiet when there is nothing to send. A non-zero value is the number of seconds of no link activity that will be allowed before RR is sent with the P bit. The remote system must respond to this poll within the T1 value.

toa/npi No
TOA/NPI indicates an alternate format for calling and called addresses, which are specified in the call setup.

Type of Address/Numbering Plan Indicator. There are two formats for an address block, regular and TOA/NPI. Non-TOA/NPI formats are supported by all networks. If you decide to use the TOA/NPI format you must first have an agreement with your network provider (known as a subscription time option) to support TOA/NPI address blocks so that addresses will be readable.

tx_password blank See rx_password.

window_send 2 Default send window size.

window_recv 2 Default receive window size.

window_neg YES Flag. Allows window negotiation on incoming calls.

window_max 7 Maximum window size to automatically negotiate down to.

zerocause YES DTE/DCE Independent Flag. Forces all cause bytes to be transmitted as 0. You should enable if DTE, and disable if DCE.

Revision 6.1.0 (February 2003)